This invention relates generally to a system and method for monitoring process and environmental parameters in a manufacturing or other process and in particular to a monitoring system for a process where it is not possible to use conventional monitoring methods due to movements of the monitored object.
It is desirable to be able to monitor various process and environmental parameters associated with a process to determine how well the process is functioning. For example, the temperature of a CVD (chemical vapor deposition) process (a critical parameter associated with the CVD process) may indicate the quality of the film being deposited by the CVD process at the time in question. For a non-moving object, there are many conventional process monitoring systems which permit various parameters to be determined. Unfortunately, it is difficult for such a conventional system to be used with a object that is moving during the process in question. To better understand the problem, an example of a particular moving object (e.g., a reticle in a semiconductor manufacturing process) that needs to be monitored will be described, but it should be understood that the problem is associated with any moving object that needs to be monitored.
A reticle in a semiconductor manufacturing process is a specially made photo xe2x80x9cnegativexe2x80x9d used to expose a photosensitized semiconductor wafer prior to etching in order to ultimately produce a plurality of integrated circuits (IC) on the semiconductor wafer. A typical reticle is made of quartz with thin chrome traces on it representing the desired electrical connections for the particular IC. Modern reticles with small geometry (e.g., very fine lines and a small spacing between the lines corresponding to the very close electrical traces on modems ICs) are particularly sensitive to various environmental and process parameters, such as exposure to electrostatic voltages. As a result of this exposure, the thin traces on the reticle can be damaged or destroyed and the process engineer may not realize that the reticle has been damaged.
Even a small number of damaged reticles can cause disproportionately large losses because the damaged reticles can go undetected and be used in a photolithography process to produce a large number of defective ICs, which are expensive to manufacture. Further, in addition to replacement costs of defective ICs and reticles, the down time of a fabrication facility may significantly add to the losses. Thus, it is necessary to detect and replace defective or damaged reticles from the semiconductor fabrication process as early as possible. Unfortunately, the sources of electrostatic damage for reticles are varied and unpredictable because reticles go through a number of different handling stages for use in a semiconductor fabrication process. For example, reticles stored in a storage place must be retrieved and loaded into a loader. Then the reticles are loaded from the loader to a stepper that is used in a photolithography process. After use, reticles are unloaded from the stepper back into the loader and carried back to the storage place. Reticles also go through several testing stages where they are subjected to various physical tests.
If a reticle comes into close proximity with an electric charge bearing object during any of the handling or testing stages, it may sustain electrostatic discharge damages. For example, the test pads on which the reticles are placed may be a source of electric discharge. Even if the reticle does not sustain an immediate electrostatic discharge damage, the effect may accumulate in the reticle, so that the reticle becomes more and more vulnerable to electrostatic discharges.
Thus, it is desirable to provide monitoring capability for reticles"" exposure to electrostatic damages so that the process engineer would be able to identify and inspect exposed reticles in order to detect damaged reticles prior to beginning the fabrication. The monitoring would also permit the process engineer to identify specific occurrences of exposure in order to try to reduce those exposures in the future. The problem with using typical monitoring system is that the reticles travel throughout the semiconductor fabrication facility and it is impossible to monitor them at all times with stationary monitors.
Some attempts have been made to provide portable data storage systems that can travel along with the reticle in the reticle storage pod, such as Smart-Tag system by Asyst. This system consists of a miniature data storage device and an RF-ID module that can communicate with a corresponding stationary device that reads and writes data into the tag that moves with the reticle. This system, however, does not observer or record any in-process parameters.
Other conventional devices provide rudimentary means for recording parameters such as exposure to electrostatic charges. An example of it is the xe2x80x9cEx-Modxe2x80x9d device by Ex-mod Corporation and Static Bug by ElectroStatic Designs. These devices must be installed on the host (i.e. on a circuit board or a wafer) that goes through the process. They provide indications that a parameter (e.g., electrostatic exposure) has exceeded a certain level somewhere along the process. However, they do not provide information to correlate collected data points to a specific step in the process or a time frame during the process. Thus, data provided by conventional monitoring devices are difficult to interpret and analyze. Also the conventional monitoring devices are difficult to reset, and they must be completely replaced for re-use.
Thus, it is desirable to provide an in-situ monitoring of various parameters, such as electrostatic discharges and damages, that overcomes the above limitations and problems with conventional monitoring systems. It is also desirable to provide a data logger system so that parameters monitored in situ may be logged and communicated for further processing. It is to these ends that the present invention is directed.
The present invention provides a device for in-situ measurement and recording of various environmental parameters in a manufacturing process such as a semiconductor fabrication process. The device comprises sensors for detecting the parameters and converting them to sensor outputs; and a data logger coupled to the sensors for receiving the sensor outputs and logging them in a file. The device may also comprise an analog to digital converter to convert the sensor outputs to digital data and a communication module to communicate the digital data with other devices or to a centralized base station.
The communication module may comprise an RF (radio frequency) transmitter and a receiver to allow operators to interact with the device for downloading of the collected data and control of the device. The sensors on the device may include an electrostatic field sensor to detect and measure a presence or change in electrostatic field, and an electrostatic discharge sensor to detect and measure an electrostatic discharge. The data logger permits the device to continuously monitor and collect the necessary sensor data as well as timestamp them. The timestamped sensor data can be downloaded at a convenient time for subsequent analysis. Alternatively, the collected data may be presented on a built-in visual display for immediate inspection.
When applied to reticles used in a semiconductor fabrication process comprising a plurality of stages, the device may be used to monitor electrostatic field and electrostatic discharge (ESD) activities around the reticle, convert the monitored parameters into data, and log the data along with an identification of each individual stage. Logged data can be retrieved and analyzed to determine the time and location of detrimental activities such as electrostatic discharge on reticles. When there is a combined occurrence of electrostatic discharge and electrostatic field from the monitored readings, it is likely to indicate a valid local ESD event. Extraneous electrostatic discharges may be filtered and excluded using various criteria based on the sensor outputs.